As a kind of frequency selecting devices, cavity filters are widely used in the communication field. Because of the special requirements on signal transmission of the cavity filters, interconnections of individual components of such a cavity filter with each other and with external connectors are required to be very precise.
Referring to FIG. 1, there is shown a schematic partial cross-sectional view of a cavity filter in the prior art, where a part of an external circuit board connected with the cavity filter is also shown.
As shown in FIG. 1, the cavity filter comprises a cavity 100, a cover plate 110, a connector outer conductor 120 and a connector inner conductor 130.
Briefly speaking, the cover plate 110 covers the cavity 100. The connector outer conductor 120 is connected with the cover plate 110, and the connector inner conductor 130 is disposed inside the connector outer conductor 120 and passes through the cover plate 110 to be connected with a signal transmission point of an external circuit board 150 outside the cavity filter. Generally, the connector outer conductor 120 and the connector inner conductor 130 are designed to be coaxial with each other to form a signal transmission structure. The connector outer conductor 120 is further provided with an electrically conductive isolation adhesive 124 to prevent signal leakage.
In the process of researching and practicing of the prior art, the present inventor has found that, in the prior art, there are the following problems because of the manufacturing errors and device errors of the inner conductor 130 and the circuit board 150: if a height of the inner conductor 130 is lower than an assembly reference level, a gap h usually results therebetween to cause distortion of the circuit board after the inner conductor is connected with the circuit board; and if the height of the inner conductor 130 is higher than the assembly reference level, the inner conductor 130 will lift the circuit board 150 up to also cause distortion of the circuit board 150. This makes it impossible to keep good touch between the connector inner conductor 130 and the signal transmission point of the external circuit board 150 outside the cavity filter.